1. Field of the Invention
This invention relates to optical networks and in particular to optical networks in which an optical waveguide of a given refractive index profile has a waveguiding core surrounded by a cladding to which is coupled a source of optical information signals at a first wavelength, an optical amplifier, and a source of optical pump power at a second wavelength shorter than the first wavelength for optically pumping the optical amplifier.
2. Related Art
It is envisaged that optical networks will be made from various types of optical waveguides and optical amplifying technologies, for example, planar Si--SiO.sub.2 waveguides, plastics or polymer based fibre guides, planar doped waveguide amplifiers and so on.
A particular example of such a network is described in the applicant's co-pending patent application WO 90/09708 published on the 20 Aug. 1990 which network is designed to provide a multiple access interconnection scheme which can be exploited for both static and dynamic interconnect applications. This network is based on optical fibre waveguides. The teaching of this patent application is imported in full into this application by reference.
The spatial dimension of such an interconnection network can be based on optical D-fibres, for example. See for example Cassidy S. A. et al, 1989 "Extendable Optical Interconnection Bus Fabricated using D-Fibre" IOOC 1989, Kobe, Japan, Paper 21 D2-1 pp 88-89. A central component of the design is a multi-fibre backplane for carrying the signals and the reference channels, with discrete tapping points along its length. These tapping points may take the form of array connectors in the known form of crossed D-fibres. The interaction length is determined by the angle of crossover of the crossed D-fibres. Each connector provides a link between each output fibre and its corresponding fibre path on the backplane, evanescently tapping out a small portion of the power from each of the signal and reference channels. The limitation on the number of the tapping points is that eventually the signal level along the backplane will fall below detector levels (as each tap removes a small portion of signal).
The use of erbium doped fibres, either distributed or in discrete amplifier units, allows amplification of the signal in the 1.55 .mu.m window. The amplification can be arranged to maintain the output from all the tapping points on the bus above the detector power limit. The signal power is regenerated by amplification between tapping points, thus allowing a significantly larger number of user ports to be served. It is convenient to distribute the pump power along the waveguide to the fibre amplifiers from a single pump source rather than provide a separate pump source for each amplifier. However, a small amount of pump power will also be removed at each tapping point and so wasted.